Several types of nmr data depend upon internuclear distances and the details of molecular motion. These include spin-lattice relaxation rates, spin-spin relaxation rates and perturbation of signal intensities by nuclear Overhauser effects. Analysis of such information can provide useful insights into protein structural features in solution and possibly will be applicable in studies of proteins on membrane-surfaces. A number of technical and interpretational impediments to the application of these experiments in protein systems can be overcome by the introduction of fluorine atoms into the protein structure; this can be accomplished by covalent modification of amino acid residues or by biosynthetic incorporation of fluorine-containing amino acids. Small molecule binding sites on proteins can be examined by the same approaches when fluorine nuclei are placed on the interacting small molecule. In favorable circumstances, the experiments indicated should (1) identify the type(s) of amino acid residues near the fluorine nucleus, (2) provide some indication of the distances between these amino acids and the fluorines, and (3) produce estimates of the time-scales for molecular motions near the fluorine atoms. With small molecule-protein complexes the rate of dissociation of the complex can also be determined by these methods. The experimental work will focus largely on rabbit proteins which contain fluorinated amino acids and serine proteases which have been covalently modified.